Depends on what kind of cable on your 500' run.
Shielded cable, try Earth ground on the shield on both ends.
I have got away using Cat-5 cable for audio with a 100' run.
Use 2 cables 1 for Tx and 1 for RX to prevent cross talk.
Cat -5 has 4 pairs of wire, solid colors all + and stripes all -
connected together to minimize resistance.
Twisted Pair does a great job of inducing RF voltage equally on each
wire so there is no difference potential on each wire.
Ran speaker level audio through the wire then reduced the audio level to
mic level with 2 resistors at the radio mic and sound card mic, 100 ohm
in series with the *+* and 10 ohm to audio* *minus* *as a voltage divider.
+ and - audio come from across the 10 ohm resistor.
That reduced the audio level to 1/10 its original level, and at the same
time reduced any interference
on the audio line by the same factor of 10.
Depending your audio levels you may be able to go as high as a 1K in
series with the 10 ohm.
That will reduce the audio and interference by a factor of 100.
Another thing to try may be as simple as a ferrite toroid on both ends
of the wire.
They will act like an RF Sponge.
Another thing to try, .001 or .01 cap across the mic inputs, depending
on the impedance of your audio circuit.
Wrong cap will affect your high audio frequencies.
May take some playing around but you can beat the interference.
N3FLR - Frank
On 11/21/2007 12:21 PM, Mike Morris WA6ILQ wrote:
At 05:58 AM 11/21/07, you wrote:
(big chunk cut out)
Al published my EchoLink interface on his web site
(the PSE508 web site) that used the PSE-508. I had a
500 ft cable between the computer and the repeater
using this interface which worked OK until a
high-power AM broadcast station came on line about 5
miles from my location. I had audio from the BC
station on the input of my repeater and also on the
EchoLink audio to the internet. I will have to go to
an RF in-band link to eliminate the problem as I was
not able to get rid of it on the long cable.
73 - Jim W5ZIT
Rather than go to all the trouble of setting up the RF link, maybe we
can help you get the broadcast interference out of the cable. After
all, the telecom industry has been getting RF out of long cable runs
for over a century.
The info in this writeup may help...
Mike Sandman has a wholesale telephone equipment distribution company
in the Chicago area.plus he
has a telecom service company... and he has done a number of
interesting things... look at
www.sandman.com <http://www.sandman.com/>...
but his RF elimination page is good. See <
http://www.sandman.com/pdf/Page43.pdf>
Unfortunately his company is up for sale, I hope the web site does not
go away...
Mike WA6ILQ
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